Compensating-pressure piston and cylinders for gas compressors and expanders



3,204,864 FOR GAS TORS #Z WK LAKER JOHN G. DAUNT BY ATTORNEY Sept. 7, 1965 s. F. MALAKER ETAL COMPENSATING-PRESSURE PISTON AND CYLINDERS COMPRESSORS AND EXPANDERS Filed June 3, 1963 United States Patent Jersey Filed June 3, 1963, Ser. No. 284,969 2 Claims. (Cl. 230-172) This application is a continuation-in-part of copending application Serial No. 241,221, filed on November 30, 1962, by Stephen F. Malaker and John G. Daunt, now Patent No. 3,128,605.

This invention relates to a new design for a piston and its associated cylinder suitable for gas compressors or expanders. More specifically, it deals with a piston and cylinder design which creates a pressure-compensating volume, designed to minimize blow-by of gas from the compressor or expander volume above the head of said piston through the space between the piston and said cylinder walls.

These are increasing requirements for compressors and expanders which can operate without lubrication of the piston reciprocating in its cylinder. Examples of these requirements are found in cryogenic engineering where it is necessary to avoid contamination by oil of the cryogenic working gases, since oil may solidify and cause blockages or malfunctions of the low temperature parts of the systems. In other areas of engineering, such as those associated with pumping of hazardous chemicals or of gases which need be maintained in a high state of purity, there are increasing demands for eflicient compressors or expanders, the pistons of which reciprocate in their cylinders Without lubrication. For these oil-free requirements our invention is most particularly applicable. It is to be noted that in oil-free operation of such compressors or expanders a compromise must be made between piston ring wear and blow-by past the rings. The novel piston and cylinder arrangement of this invention minimizes greatly the blow-by by the inclusion of a pressure-com pensating volume.

A preferred embodiment of the present invention is illustrated by the accompanying drawing in which FIG- URE 1 shows a perspective side elevational view, partly in cross-section of a portion of compressor embodying the invention. The drawing confines itself to a description of only one such said piston and cylinder and which for simplicity omits a detailed manifestation of the driving means whereby said piston is caused to reciprocate in said cylinder. Referring to the drawing, numeral 2 refers to the working piston which is caused to reciprocate in cylinder 3 by action of connecting rod 4, which is acted upon by a suitable crank 21 of a driving means which latter, for simplicity, has been omitted in the drawing. The gas to be compressed or expanded is introduced into working space 5, formed by the cylinder head 6 and the top of piston 2 through suitable port, ports, or conduits 7. Piston 2 at its lower end is increased in diameter, the lower larger diameter portion 8 being referred to as the pressure-compensating piston. The lower end 22 of cylinder 3 is made of a diameter larger than that of cylinder 3 to accommodate the pressure-compensating piston 8 and is referred to as pressure compensating cylinder 9. Piston rings 10 are located in the upper part of piston 2, and serve to seal the annular space between piston 2 and cylinder 3 from flow of gas into or out of working volume 5. In the preferred embodiment, piston rings 10 are nonlubricated, oil-free rings made from glass-filled fluoropolymer material (e.g., that sold commercially under the name Tefion). Pressure compensating piston 8 carries Bidififid Patented Sept. 7, 1965 piston rings 11 which also may be non-lubricated, oil-free rings. In this embodiment, it is arranged that rings 10 have the lightest possible spring loading against the Walls of cylinder 3 consistent with moderate prevention of blowby, whereas rings 11, which could, if necessary, be oillubricated, have greater spring loading. Pressure compensating piston 8 riding in its cylinder 9, which is disposed in coaxial relation with cylinder 3, and provides, at the end of its upper stroke, pressure compensating volume 12, which, as illustrated in FIGURE 1, is a closedoff space to be filled with the same fluid as permeates working volume 5. The compression ratios of working volume 5 and pressure compensating volume 12 are chosen in the design to be such that the pressures in volumes 5 and 12, as a function of piston displacement, are in first approximation the same. By this design the pressure difference across the critical piston rings, namely piston rings 10, is minimized, thus minimizing unwanted blow-by past these rings.

A further feature of the invention is that, by making piston 2 integral with compensating-pressure piston 8, compensating piston 8 serves also as a cross-head thus minimizing side thrust of piston 2 on the walls of cylinder 3 and increasing the efiiciency of the gas sealing rings 10 and increasing the mechanical life of the system.

Several methods may be adopted for charging pressurecompensating volume 12 with its appropriate gas and recharging it to compensate for losses of such gas during opera-tion, two of which are illustrated in FIGURE 1. The first method operates in the following manner. Bleed pipe 13 communicates with working volume 5, at the time piston 2 is at bottom dead center, through hole 14 suitably located in the wall of cylinder 3. Pipe 13 is connected to one-way valve 243 which permits flow of gas through it from pipe 13 to pipe 15 when there exists a small diiference of pressure across said valve. Pipe 15 communicates to pressure-compensating volume 12, when said pressure-compensating volume is at its maximum, through hole 16, suitably located in the Wall of pressurecompensating cylinder 9. An alternate method of filling, as shown by the broken lines in the drawing of FIGURE 1, may be adopted in the case in which crank-case 17 attached to the lower end of pressure-compensating cylinder 9 is of a gas-tight hermetically-sealed type. Such a crank-case may be filled with the same gas as the gas working in working volume 5 and may act as a supply of gas for pressure compensating volume 12, such gas flowing from crank-case 17 through pipe 18, through one-Way valve 19, and thence into said pressure-compensating volume through hole 16, as described above.

One application of this invention has been made in the construction of refrigerating engines operating according to a modified Stirling cycle and has been found to improve markedly its performance, since any blow-by of H gas past the expander piston in such an engine reduces considerably the refrigerative load which can be handled by the engine. Other applications of the invention, as aforesaid, are of significance for expanders and compressors which require to operate with oil-free, non-lubricated piston rings.

We claim:

1. A compensating-pressure piston and cylinder for gas compressors and expanders, comprising,

a working piston,

a close-fitting working cylinder, having a cylinder head, and in which cylinder said piston is designed to reciprocate and having a working space between said piston and cylinder head,

a second piston of larger diameter than that of the working piston and joined to the lower portion of said latter piston,

a close-fitting second cylinder of larger diameter than that of the working cylinder, said latter cylinder having a partial cylinder head and said latter cylinder being joined to the lower portion of said working cylinder to accommodate said second piston, and providing a closed-in blow-by minimizing compensating pressure volume between its head and that of the second piston in a manner such that the compression ratios of the working space and the compensating-pressure volume are approximately the same,

a bleed line connecting said Working volume with said pressure-compensating volume, and i a one-way valve disposed in said bleed line and designed to permit said pressure-compensating volume to acquire a pressure approximately equal to that in said working volume.

2. A compensating-pressure piston and cylinder for gas compressors and expanders, comprising,

a crank-case filled with pressurized gas,

a crank in said crank-case connectable to a working piston to reciprocate same,

a working piston connected to said crank,

a close-fitting working cylinder, having a cylinder head, and in which cylinder said piston is designed to reciprocate, and having a working space between said piston and the cylinder head,

a second piston of larger diameter than that of the 4. working piston and joined to the lower portion of said latter piston,

a close-fitting second cylinder of larger diameter than that of the working cylinder, said latter cylinder having a partial cylinder head, and said latter cylinder being joined to the lower portion of said working cylinder to accommodate said second piston, and providing a closed-in blow-by minimizing compensating-pressure volume between its head and that of the second piston,

a bleed line connecting said compensating-pressure volume and said crankcase, and

a one-way valve disposed in said bleed line and designed to permit said pressure-compensating volume to acquire apressure approximately equal to that v in said working volume.

References Cited by the Examiner UNITED STATES PATENTS 1,467,489 9/23 Nordberg 230-183 X 2,696,413 12/54 Wheildon 230206 X 2,978,986 4/61 Carder et al. 23056 X 3,112,060 11/63 Ollier et al. 230-56 FOREIGN PATENTS 258,194 4/28 Italy.

LAURENCE V. EFNER, Primary Examiner.

ROBERT M. WALKER, Examiner. 

1. A COMPENSATING-PRESSURE PISTON AND CYLINDER FOR GAS COMPRESSORS AND EXPANDERS, COMPRISING, A WORKING PISTON, A CLOSE-FITTING WORKING CYLINDER, HAVING A CYLINDER HEAD, AND IN WHICH CYLINDER SAID PISTON IS DESIGNED TO RECIPROCATE AND HAVING A WORKING SPACE BETWEEN SAID PISTON AND CYLINDER HEAD, A SECOND PISTON OF LARGER DIAMETER THAN THAT OF THE WORKING PISTON AND JOINED TO THE LOWER PORTION OF SAID LATTER PISTON, A CLOSE-FITTING SECOND CYLINDER OF LARGER DIAMETER THAN THAT OF THE WORKING CYLINDER, SAID LATTER CYLINDER HAVING A PARTIAL CYLINDER HEAD AND SAID LATTER CYLINDER BEING JOINED TO THE LOWER PORTION OF SAID WORKING CYLINDER TO ACCOMMODATE SAID SECOND PISTON, AND PROVIDING A CLOSED-IN BLOW-BY MINIMIZING COMPENSATING PRESSURE VOLUME BETWEEN ITS HEAD AND THAT OF THE SECOND PISTON IN A MANNER SUCH THAT THE COMPRESSION RATIOS OF THE WORKING SPACE AND THE COMPENSATING-PRESSURE VOLUME ARE APPROXIMATELY THE SAME, A BLEED LINE CONNECTING SAID WORKING VOLUME WITH SAID PRESSURE-COMPENSATING VOLUME, AND A ONE-WAY VALVE DISPOSED IN SAID BLEED LINE AND DESIGNED TO PERMIT SAID PRESSURE-COMPENSATING VOLUME TO ACQUIRE A PRESSURE APPROXIMATELY EQUAL TO THAT IN SAID WORKING VOLUME. 